A Search for Clustering around Herbig Ae/Be Stars

Background

It is a well know result that young stars are not found to form in isolation, but in groups and aggregates. However, while low mass stars are usually found to form in loose groups with densities of a few stars per cubic parsecs, high mass stars are known to form in dense clusters with up to 10000 stars per cubic parsec.
We decided to study the onset of the star formation in clusters at the intermediate mass level. We have undertaken a survey of a cospicuous number of fields around intermediate mass young stars (Herbig Ae/Be stars, HAeBe) with the aim of detect and characterize the groups of young stars that may have formed together with the HAeBe star.
We chose to observe the fields in the three Near infrared J, H, and K broad bands following the idea that the clusters we are looking for are probably embedded in the parental molecular cloud and hence not easily observable at optical wavelengths.

Observations

The observations have been (and are being) carried out using the Arcetri Near Infrared CAmera (ARNICA) at the TIRGO and NOT telescopes.
A few NIR "true color" images from TIRGO and K-band images from NOT are linked at the end of this document.

Achievements

Up to now 45 fields around HAeBes have been observed. The first results obtained toward 19 fields have been published in: Testi L., Palla F., Prusti T., Natta A., Maltagliati S. 1997, A&A, 320, 159 (paper I).
In paper I several cluster identification methods are described and compared. A Richness Indicator Ic that counts the effective stars above the background is defined.
From the first sample of 19 objects presented in paper I there is a hint that the onset of clustering at the intermediate mass level is not a smooth transition, but detectable clusters appear only around stars earlyer than B5-B7.

Status

Data reduction and analisys for the whole sample has been completed and you can check the current Ic vs. Sp.Type plot here:

Nov 1997

Pictures

Here are some nice NIR truecolor pictures from the first runs at TIRGO:

LkHa 25 - a confuse field.

LkHa 25 - a nice, tiny group.

BD +404124 - A rich, compact cluster.

And here some from the Aug-Sep 1996 run at NOT, each image is ~8.5 arcmin wide (K-band):

AS 310 - a preatty crowded field.

BD+651637 - a gorgeous cluster.

HD 200775 - nice nebula!

HD 278937 - a rather empty field.


Mantained by: Leonardo Testi

Last update: 16 May 1997